The role of the synaptic transmitter substance in the visual system is to be investigated. The first objective is to work out the role of the various synaptic transmitters that have been localized to particular cells in the retina. The rabbit will be used, because of the large variety of types of receptive field found in the retina. Recordings will be made from ganglion cells, and the changes in their receptive fields will be observed when transmitter substances or their antagonists are applied. The second objective is to work out the role of noradrenalin in the effects of visual deprivation on the visual cortex, particularly deprivations other than eye closure, where the critical period is different from the critical period for eye closure. Noradrenaline and 6-hydroxydopamine will be applied to the visual cortex of kittens under various kinds of deprivation, recordings will be made from cells in the visual ccrtex and results in normal animals compared with results in animals with drugs applied.